Industrial oven and method of operating the same

ABSTRACT

An industrial oven is provided in its circumferential wall with a first group of burners so arranged that when they operate they inject into the chamber of the oven combustion gases which form therein a first coil filling the chamber and rotating in one direction. A second group of burners is also provided in the wall and so constructed that they inject into the chamber combustion gases which form a second coil therein which fills the chamber but which rotates in an opposite direction.

United States Patent 1191 Knaak [451 Apr. 10, 1973 1 INDUSTRIAL OVEN AND METHOD OF OPERATING THE SANIE [75] Inventor: Rudiger Knaak, Neuss, Germany [22] Filed: Feb. 25, 1971 [21] Appl. No.: 118,812

[30] Foreign Application Priority Data 3,172,647 3/1965 Remmey ..263/28 3,485,900 12/1969 Cremer et 2,191,438 2/1940 Breeler Primary Examiner-John J. Camby AttorneyMichael S. Striker ABSTRACT An industrial oven is provided in its circumferential wall with a first group of burners so arranged that when they operate they inject into the chamber of the oven combustion gases which form therein a first coil filling the chamber and rotating in one direction. A

Mar. 3, 1970 Germany ..P 20 09 761.4 Second g p of burners is also provided in the Wall [52] Us. Cl 432/25 432/9 432/52 432/176 and so constructed that they inject into the chamber 432/196 combustion gases which form a second coil therein [51] Int Cl F27) 3/10 F27b 9 /26 which fills the chamber but which rotates in an op- 58 Field of Search ..263/28, 40, 43, 52 pslte dlrecmn- [56] References Cited 10 Claims, 6 Drawing Figures UNITED STATES PATENTS 2,492,942 12/1949 Stoler ..263/40R INDUSTRIAL OVEN AND METHOD OF OPERATING THE SAME BACKGROUND OF THE INVENTION The present invention relates generally to an industrial oven, and more particularly to an industrial oven for heating and heat-treating of workpieces, and to a method of operating such an oven.

Ovens are known for heating and heat-treating of metallic or other workpieces. Generally speaking, it is perhaps the primary consideration of such ovens that the workpieces are heated as evenly as possible. This is particularly important in order to obtain uniform material characteristics in the workpieces after heat treatment and annealing processes. Another reason for this requirement is to obtain uniform characteristics of material behavior during subsequent heat-deformation that is when the material is subsequently formed in heated conditionand also for limiting the development of heat tensions in these materials or workpieces.

Evidently the uniformity with which such workpieces are heated depends upon a variety of factors. One of these is the construction of the oven itself. Another is the construction and arrangement of the heating means for heating the oven. A further one is the particular type of workpiece to be heated and the position thereof in the oven, as well as the speed of heating and cooling involved.

The problem being known, various attempts have been made to provide for maximum uniformity of heating. One well known and quite efficient approach to the problem is to make the temperature in the oven and the temperature in the workpieces to be heated uniform by withdrawing the atmosphere in the oven by means of blowers or the like and re-introducing it into the oven at suitable locations. In other words, there is a turnover of air which is recirculated into the oven at such points where it is considered to be of most importance. However, this is a relatively expensive proposition in terms both of the complexity of equipment involved and of operating costs; in addition, where higher temperatures are involved, this approach cannot be used.

If the requirement for temperature uniformity is not very strict, it is sufficient to provide in the oven walls a large number of burners which are then individually adjusted depending on the local heat requirements. However, especially if the oven is of relatively substantial width and if the burners are not particularly strong, that is if they have a short flame pulse, in this construction the thermal lift of the hotter burner gases becomes quite noticeable, meaning that the hot combustion gases have a tendency to move upwardly along the walls and to collect at the underside of the oven roof. This means that the oven obviously becomes hotter in the upper regions than in the lower regions so that this solution is usually not suitable where the requirements for evenness of temperature are strict.

On the other hand it was found that a substantial improvement could be obtained by using high-speed burners which inject their combustion gasesat high speed into the chamber of the oven, and also in a condition in which they are already largely combusted. The strong pulse or impulse of the stream of combustion gases ejected from the burner and injected into the oven chamber, causes a thorough admixture and agitation of the atmosphere in the oven. This tends to in effect throughout the oven, substantially uniform heat transfer to the workpiecesand thereby substantially uniform workpiece temperatures-are obtained. In this construction the arrangement of the burners is of no particular importance. However, the high-speed combustion gases which travel relatively far into the interior of the oven chamber, should not directly impinge upon the workpieces to be heated, and for this reason it is preferred to so arrange the high-speed burners that their stream of combustion gases upon injection into the chamber moves along one of the walls bounding the latter. It is quite customary to provide in the side walls of such ovens a row of burners each, whose streams of combustion gases are so oriented as to move horizontally and with low distance above the hearth of the oven. It must be kept in mind that in such constructions the workpieces to be treated must not interfere with the development of the streams of combustion gases. Therefore, particularly if the workpieces are of large dimensions or elongated, they must be positioned at adequately large spacing from the hearth by utilizing supports which afford this spacing.

Frequently the burners are also arranged in banks adjacent the hearth in such a manner that the stream of combustion gases moves vertically upwardly along the side walls. In special cases, and in particularly large ovens, it has also been known to provide additional burners which are then so oriented that their stream of combustion gases moves horizontally beneath the oven roof.

As the heat requirement decreases, the impulse or pulse of the stream of combustion gases decreases correspondingly. This means that the equalizing effect of the high-speed burners becomes the less effective, the more the burner is throttled. This is avoided in that the temperature regulation is effected not by throttling the burners, but by switching them on and off as required. In such a construction the burners may be so arranged that their streams of combustion gases are directed more or less towards one another. However, they may also be offset so that the stream of combustion gases from one burner is directed towards a gap between the streams of combustion gases from two oppositely located burners. There is no really significant difference between these two arrangements because the stream of combustion gases undergoes, as it moves away from the outlet of the respective burner, the substantial widening which is a result of aspiration of the surrounding atmosphere and which is well known to those skilled in this field. This means that at some distance from their respective burner outlets, the streams of combustion gases will overlap in any case, no matter how they are directed.

In certain instances the admixture and agitation of the combustion gases, and particularly the rolling or turning over in the chamber of the oven, can be improved substantially in that the burners are so arranged that the impulse of the respective streams of combustion gases causes a rotation effect of the combustion gases in the chamber, leading to the development of the coiled rotating flow of'the combustion gases. However, it has been found that although this further improves the uniformity of temperature in the oven, this approach is omitted in actual practice for certain reasons to specific applications, for instance in so-called shaft furnaces in which an elongated substantially cylindrical workpiece is arranged in upright position and located in a similarly cylindrical oven housing. This makes possible a good and adequate flow of combustion gases about the workpiece with complete symmetry of heating. In most applications, however, the oven is not sufficiently symmetrical, nor are the workpieces arranged sufficiently symmetrically within the oven, to permit the utilization of this approach where a single rotating coil of combustion gases is created. In certain applications or ovens the differing quality in the aligning of hearth and oven walls, and also the arrangement of the workpieces of the hearth, necessitates the lack of sym' metry which cannot be overcome even if the workpieces are not located directly upon the hearth but instead are spaced from it by suitable supports. It must be taken into account, of course, that configurations and sizes of workpieces vary greatly which brings with it in particular the danger that the burners which direct a stream of combustion gases from one side transversely of the hearth in order to obtain the rotating spiral or coil of combustion gases, will heat the underside of the workpieces unevenly at the two opposite sides of the oven.

Thus, none of the aforementioned prior-art approaches are entirely satisfactory.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the aforementioned disadvantages.

More particularly it is an object of the present invention to provide an improved industrial oven which is not possessed of the disadvantages of the prior art and which permits the even and uniform heating of workpieces therein.

A concomitant object of the invention is to provide a method of operating such an oven.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides, in an industrial oven, in the combination of wall means defining an internal chamber, a first group of burners and a second group of burners. The first group of burners is provided in the wall means and operative for injecting into the chamber combustion gases which form a first helix of combustion gases which fills the chamber and which rotates in one direction about its longitudinal axis. The second group of burners are also provided in the wall means but are operative for injecting into the chamber combustion gases which form a second helix of combustion gases which also fills the chamber but rotates in an opposite direction about its longitudinal axis.

This approach makes it possible to utilize the advantages of a rotating-helix combustion gas in ovens other than the aforementioned shaft-type oven. The

groups of burners are preferably'operated alternately,

that is first one group and then the other, but if the heat requirements are very high, it is advantageous if the burners are so constructed that they can'al'so be operated simultaneously.

The novel features which are considered as characterist'ic for the invention are set forth in particular in I the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic transverse sectional elevation of one embodiment of the invention;

FIG. 2 illustrates the embodiment of FIG. 1 during a different operating stage;

FIG. 3 is a view similar to FIG. 1 but illustrating a further embodiment of the invention;

FIG. 4 illustrates the embodiment of FIG. 3 in a different stage of operation;

FIG. 5 is also a view similar to FIG. 1 but illustrating still another embodiment of the invention; and

FIG. 6 illustrates the embodiment of FIG. 5 in a different stage of operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail, and firstly FIGS. 1 and 2 thereof, it will be seen that reference numeral 1 identifies the wall means or housing of the oven which defines within it the oven chamber. The reference numeral 2 identifies a hearth carriage with the wheels 3 provided thereon, and on the carriage 3 there is supported a workpiece (here illustrated in cylindrical configuration) which is supported on the hearth carriage via supports 5.

The illustrated oven has a first or left group of burners 6 and a second or right group of burners 7. In longitudinal direction in which the hearth carriage 3 can move, that is normal to the plane of the drawing, the oven may have any desired length and may be subdivided into separate zones for temperature-regulating purposes.

In FIG. 1 the arrows indicate that the left-hand burner group is operating, with all burners operating together and injecting into the interior of the oven chamber a stream of combustion gases which forms in the chamber a helix of combustion gases elongated longitudinally of the oven 1 and rotating in counterclockwise direction. The helix rotates about and surrounds the workpiece 4 and fills or substantially fills the interior space of the oven.

Conversely, FIG. 2 shows that the other or righthand burner group is operating, causing a similar helix of rotating combustion gases but which, as indicated by the arrows in FIG. 2, rotates in clockwise direction counter to the direction of rotation of the helix in FIG. 1. Thus, any unevennesses in heating of the workpiece which may have resulted during the operation of the burners of group 6 are compensated-for by operation of the burners of group 7.

It is advantageous according to the present invention that the burners are high-speed burners of known construction which are of such type that the combustion gases leave the burner at a speed of better than 50 m/sec. Also, it is preferable that the regulating of ternperatureswhen it is no longer necessary for the burners to operate continuouslybe carried out not by throttling of the burners but instead by switching them on and off as required to obtain the desired temperature regulation. This avoids the problem which has been discussed earlier herein.

Coming to the embodiment in FIGS 3 and 4 it will be seen that here again the oven is substantially the same as in FIG. 1. The cross-sectional configuration differs somewhat, and the workpieces are somewhat different although also cylindrical. However, these features are only obvious differences from the configuration in FIG. 1. What is the major difference in terms of the'present invention, of the embodiment in FIGS. 3 and 4 over that in FIGS. 1 and 2, is the fact that in FIGS. 3 and 4 the burners 8which reference numeral here is representative of the first and second group of burnersare supplemented by additional groups of burners 9 which are arranged in banks next to the hearth carriage and so oriented that they eject their streams of combustion gases upwardly rather than transversely of the oven. In the embodiment of FIG. 3 the burners'in the left-hand group 8 operate to produce the helix of combustion gases which rotates in counterclockwise direction. At the same time, the burners 9 of the righthand bank are also in operation and facilitate and add to the formation and rotation in counterclockwise direction of the illustrated helix of combustion gases.

7 In FIG. 4 the arrangement is reversed in that the burners 8 of the right-hand burner group operate, producing the clockwise-rotating helix of combustion gases, and are supplemented by the burners 9 of the left-hand bank of such burners.

FIGS. 5 and'6, finally, show still a further embodiment. Again, the oven in these Figures is basically the same as in FIGS. 1 and 2 and need not be further described. The workpieces are of different configuration from FIGS. 1, 2 and 3, 4 but this also is of no importance. The workpieces of FIGS. 1 and 3 could similarly be treated in the oven of FIG. 5.

What is different in terms of the present invention in the embodiment of FIGS. 5 and 6 over the preceding embodiments is the fact that here there are provided not only all of the burners in the embodiments of FIGS. 3 and 4 but additional burner groups similar to the burner groups 6 and 7 of FIG. 1, and the burner group 8 of FIG. 3; but arranged below the roof or ceiling of the oven. These burner groups, which have reference numeral 8a in FIG. 5, cooperate with the other burners of the other groups to produce the clockwise or counterclockwise rotating helices. In FIG. 5 the left-hand burner group 8 is operating, together with the righthand bank of burners 9, and with the right-hand burner group 8a. In FIG. 6 it is the right-hand burner group 8 which operates, together with the left-hand bank of burners 9, and the left-hand burner group 8a, to produce the clockwise rotating helix of combustion gases.

By combining the various burners in the groups identified above, it is possible to obtain the creation of the helices'rotating about their longitudinal axis and which turn over the entire volume of combustion gases in the oven chamber and thus causes the best possible temperature equalization. The difficulties which were identified above and which were inherent in terms of uneven heating due to the lack of symmetry of the oven and of the workpieces to be heated, are overcome according to the present invention by having the burners so arranged and operating them in such a manner that they will alternately produce a helix of combustion gases which will rotate clockwise and subsequently counterclockwise, or vice versa. It is of course also within the concept and scope of the present invention to so arrange the burners in groups that helices are produced having different axes of rotation in space.

If the regulation of temperature in the oven is carried out by switching the burners off and on, and if the oven is subdivided into several temperature-regulating zones which are located one behind the other in longitudinal direction of the oven, then it is conceivable that it may happen that in one zone a helix of combustion gases is created which rotates in clockwise direction whereas in an adjacent zone the helix rotates in counterclockwise direction. These oppositelyrotating helices could then interfere which would be disadvantageous. Therefore, the invention provides according to a further embodiment that the selection of the burner groups in all regulating zones which operate at any one time is controlled by a control device, such as a timer switch, so that during a predetermined time interval always'the groups of all zones are operated which willproduce a helix rotating in either the clockwise direction or in counterclockwise direction. Subsequently, when the time interval has passed, the remaining burner groups are switched on to produce a helix which operates in the opposite direction to that prevailing before.

In many instances and in many industrial ovens the heat requirements will vary during operation in wide latitudes, per time unit. For instance during the start-up a high amount of heat energy is usually required, whereas during the subsequent maintenance and equalization only a substantially smaller amount of heat energy is needed. On the other hand it is particularly important that temperature equalization be provided during this equalizing period. If the burners are throttled to obtain the temperature regulation, then the burner impulse decreases as the burner is throttled, whereas if the temperature is regulated by switching the burners off and on, the relationship of on-time to off-time becomes increasingly less advantageous as the operation of the burner proceeds. Therefore, the invention has a final concept which provides that if the oven requires at any given time a high amount of heat energy, all burner groups are operated simultaneously, but that when the oven has a small or smaller heat requirement, the burner groups are so operated as to obtain the helices which rotate alternately in clockwise and in counterclockwise direction.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in an industrial oven, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is:

1. In an industrial oven, in combination, wall means defining an internal'chamberya first group of burners provided in said wall means and operable for injecting into said chamber combustion gases forming a first helix which fills said chamber and rotates in one direction about workpieces located in said chamber; and a second group of burners provided in said wall means and operable in alternation with said first group for injecting into said chamber combustion gases forming a second helix which fills said chamber and rotates in an opposite direction about the workpieces located in said chamber.

2. In an industrial oven as defined in claim 1, wherein said burners are high-speed burners injecting said combustion gases at speeds in excess of 50 m/sec.

3. In an industrial oven as defined in claim 1; further comprising control means operatively associated with said burners for alternately operating said burners of said first group, and said burners of said second group.

4. In an industrial oven as defined in claim 3, said control means comprising timer means.

5. In an industrial oven, in combination, wall means defining an internal chamber; a first group of burners provided in said wall means and operative for injecting into said chamber combustion gases forming a first helix which fills said chamber and rotates in onedirection; a second group of burners provided in said wall means and operative for injecting into said chamber combustion gases forming a second helix which fills said chamber and rotates in an opposite direction; and control means operatively associated with said burners for operating the burners of said first and second groups alternately when the heat-energy requirement is relatively low, and for operating said burner of both of said groups simultaneously when the heat-energy requirement is relatively high.

6. A method of operating an industrial oven having an internal chamber, and a first and a second group of burners provided in the walls bounding said chamber and being respectively operable for injecting into said chamber combustion gases forming a helix filling the chamber and rotating in one or in an opposite direction, respectively, said method comprising the step of alternately operating the burners of said first group and the burners of said second group.

7. A method as defined in claim 6, comprising the step of injecting said combustion gases at speeds in excess of 50 m/sec.

8. A method as defined in claim 6, wherein the step of alternately operating said burners comprises alternately activating and de-activating said burners of said first and second groups.

9. A method as defined in claim 6, said step comprising 0 eratjng said burners of said first rou for a predeerm1ned period of time, thereupon cFe-acEvatmg said burners of said first group and activating said burners of said second group for a predetermined period of time.

10. A method as defined in claim 6, further comprising the step of operating said burners of said first and second groups in unison, at the will of an operator. 

1. In an industrial oven, in combination, wall means defining an internal chamber; a first group of burners provided in said wall means and operable for injecting into said chamber combustion gases forming a first helix which fills said chamber and rotates in one direction about workpieces located in said chamber; and a second group of burners provided in said wall means and operable in alternation with said first group for injecting into said chamber combustion gases forming a second helix which fills said chamber and rotates in an opposite direction about the workpieces located in said chamber.
 2. In an industrial oven as defined in claim 1, wherein said burners are high-speed burners injecting said combustion gases at speeds in excess of 50 m/sec.
 3. In an industrial oven as defined in claim 1; further comprising control means operatively associated with said burners for alternately operating said burners of said first group, and said burners of said second group.
 4. In an industrial oven as defined in claim 3, said control means comprising timer means.
 5. In an industrial oven, in combination, wall means defining an internal chamber; a first group of burners provided in said wall means and operative for injecting into said chamber combustion gases forming a first helix which fills said chamber and rotates in one direction; a second group of burners provided in said wall means and operative for injecting into said chamber combustion gases forming a second helix which fills said chamber and rotates in an opposite direction; and control means operatively associated with said burners for operating the burners of said first and second groups alternately when the heat-energy requirement is relatively low, and for operating said burner of both of said groups simultaneously when the heat-energy requirement is relatively high.
 6. A method of operating an industrial oven having an internal chamber, and a first and a second group of burners provided in the walls bounding said chamber and being respectively operable for injecting into said chamber combustion gases forming a helix filling the chamber and rotating in one or in an opposite direction, respectively, said method comprising the step of alternately operating the burners of said first group and the burners of said second group.
 7. A method as defined in claim 6, comprising thE step of injecting said combustion gases at speeds in excess of 50 m/sec.
 8. A method as defined in claim 6, wherein the step of alternately operating said burners comprises alternately activating and de-activating said burners of said first and second groups.
 9. A method as defined in claim 6, said step comprising operating said burners of said first group for a predetermined period of time, thereupon de-activating said burners of said first group and activating said burners of said second group for a predetermined period of time.
 10. A method as defined in claim 6, further comprising the step of operating said burners of said first and second groups in unison, at the will of an operator. 